Tungsten Clustering allows for many types of maintenance to happen with no downtime at all.
This blog post will explore how to upgrade the actual MySQL Server on all cluster nodes with zero downtime.
Zero-Downtime Upgrade Steps
This is a zero-downtime upgrade:
- Pick a replica node and shun it, and take all replication offline
- Upgrade the MySQL Server on that node
- Bring up replication and verify health
- Welcome the replica node back into the cluster
- Repeat for the other Replica node
- Perform a switch of the Primary to one of the upgraded Replicas
- Upgrade the old Primary with the same steps
The complete procedure is detailed here:
Zero-Downtime Best Practices
The best practice is to leave the cluster in Automatic mode, because shunning a node takes care of preventing both failover to the node and Connector reads from it.
Using Maintenance mode degrades the service level, because in Maintenance mode, there is no high availability (HA/automatic failover) if the MySQL Server dies.
In Automatic mode, there is HA, because the Manager still provides quorum even though the node is shunned.
Take the Replicator offline gracefully using `
trepctl offline` before taking down the database.
Bring the Replicator online and verify status using `
trepctl online` and `
trepctl services` or `
Bonus: Other Ways To Influence Cluster Behavior
Other possible ways to influence cluster behavior are the per-node Standby and Archive modes.
Standby mode allows failover to the specific node, but prevents Connector reads from it.
Archive mode prevents failover to the node, but allows Connector reads from it.
Mark a Datasource as Standby
To configure a datasource as a standby:
shell> cctrl /alpha > datasource host3 standby WARNING: This is an expert-level command: Incorrect use may cause data corruption or make the cluster unavailable. Do you want to continue? (y/n)> y DataSource 'db7-demo.continuent.com@north' is now OFFLINE Datasource 'db7-demo.continuent.com' now has role 'standby'
To clear the standby state:
shell> cctrl /alpha > datasource host3 clear standby Datasource 'host3' now has role 'slave'
Mark a Datasource as Archive
To mark a datasource as an archive:
shell> cctrl /alpha > datasource host3 set archive Datasource 'db7-demo.continuent.com' is now an ARCHIVE slave
To remove the archive role:
shell> cctrl /alpha > datasource host3 standby Datasource 'db7-demo.continuent.com' is no longer an ARCHIVE slave
In this post we summarized the zero-downtime upgrade procedure for MySQL Server in a Tungsten Cluster. We also covered best practices for upgrading, along with some bonus information about the per-node Archive and Standby modes.
For more information, please see our online documentation:
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